Expansion screws that utilize an opposing thread design have been used in orthodontic appliances for about 100 years. Typically, a central hub in the screw contains two through-holes 90xc2x0 apart. The holes allow a pin such as that designated 10 in FIG. 1 to be inserted to rotate the screw and expand two movable bodies that run on the screw threads. The spreading apart of the screw bodies effects a uniaxial extension which is incorporated into orthodontic appliances to effect a variety of treatments.
The screw is captured by a stationary component which can be a housing or simply a parallel shaft which is typically designed to allow only a xc2xc turn of the screw each time the xe2x80x98activatingxe2x80x99 pin is inserted into the central hub. To advance the screw another xc2xc turn, a single xe2x80x98activationxe2x80x99, the pin must be disengaged from the screw and reinserted. The tools or keys currently used to activate or turn such screws are very simple in design. Low cost significantly dictates the design of many high-volume orthodontic products. A straight length of wire, typically 0.040 inch in diameter, with a small loop for pinching between the fingers has been used for many years. Special plastic safety attachments are also known for preventing such keys from being swallowed.
In 1966, Soloveichik (USSR Patent No. #189,125) described a key device for turning orthodontic expansion screws consisting of a rotatable pin fitted to the end of a handle. Use of the device was also described as consisting of: 1) inserting the pin into the openings in an expansion screw, and 2) moving the handle along its long axis to rotate the pin on its axis while effecting rotation the expansion screw. Rotation of the screw is described as being related to the hinged union between the pin and the handle. Soloveichik describes the hinges as being threaded to the handle to facilitate replacement of the pin.
Schilliday (U.S. Pat. No. #5,133,659 1992) describes a similar-purposed orthodontic key consisting of a plastic handle designated 16 in FIG. 2 and freely rotating pin 18 at one end. Schilliday describes a plastic rivet for attaching the pin to the handle instead of a screw as described by Soloveichik. Both the Soloveichik and Schilliday designs have freely rotating pins (through 360xc2x0) at the end of a handle.
While such tools are simple and inexpensive to produce, it is known that the free and reversible rotation of the pin can lead to a failed activation the orthodontic screw. If the pin is not disengaged from the screw after turning the screw xc2xc turn, back-rotation of the screw can take place when removing the tool from the mouth. This reversing action negates the positive screw activation just performed.
The turning of orthodontic screws is performed at home by the patient, or the patient""s parent. Typically, the screw is turned xc2xc revolution (one activation) once or twice daily. The tool provided by the orthodontist must be simple to use and reliable to assist patient compliance and ensure that the doctor""s schedule for activation is followed. Failure to activate orthodontic screws leads to delayed treatment times and increased office visits. The steady expansion desired for this type of treatment is also affected.
The orthodontic tool of this invention functions to restrict rotation of the pin and to capture the pin at a specific angle. The tool also provides for releasing the captured pin. Capture of the pin by the tool following screw activation requires the disengagement of the pin from the screw prior to removing the tool from the mouth. This overcomes the possibility of back-driving the screw and negating the activation.
In particular, an adjusting tool and associated method of use for turning orthodontic expansion screws are described. The tool or device can comprise a contra-angled molded plastic handle or housing with a rotatable pin at the distal end for inserting into an expansion screw located in a patient""s mouth. The tool housing is designed to limit the angular rotation of the pin to the arc required for insertion and subsequent activation of the orthodontic screw. When rotated to the position associated with screw activation, the pin is captured and held in place by a locking mechanism which then requires the tool to be disengaged from the screw prior to its removal from the patient""s mouth. This feature eliminates the possibility of reversing and deactivating the expansion screw by pulling the expansion key straight out of the mouth. A manual release capability of the tool frees the pin to allow the pin to be rotated back to the insertion position after it has been removed from the mouth. A built-in light assists with sighting the end of the wire and the insertion holes in the expansion screw.
The foregoing and additional advantages and characterizing features of the present invention will become clearly apparent upon a reading of the ensuing detailed description together with the included drawing. The following detailed description of the invention, when read in conjunction with the accompanying drawings, is in such full, clear, concise and exact terms as to enable any person skilled in the art to which it pertains, or with which it is most nearly connected, to make and use the invention.